A great many aqueous dispersions of colloidal and finely divided materials are made as a result of manufacturing processes. These liquids are commonly concentrated in order to recover liquid or solids or both. By way of example, many fermentation operations require concentration of the cell broth as a preliminary step to recovery of solids for in-plant use, sale, or disposal. Such concentration is conventionally accomplished by adding a flocculant to the cell broth, followed by cross-flow membrane filtration. However crossflow membrane filtration of cells in downstream processing of fermentation broths often suffers from poor flux performance because of fouling by cells depositing on the membrane. The use of synthetic polymeric flocculants (water soluble polymers and solid particle materials) has been suggested as a means of increasing cell particle size, leading to improved fluxes. Larger particle sizes are more readily swept off the membrane surface in crossflow operation. Larger particles which do settle on the membrane form a layer which is more permeable. Thus, synthetic polymers have been shown to improve flux performance. However, due to toxic properties of several of thse polymers, they may be considered unsafe for use in the production of food and pharmaceutical products. Furthermore, there is a need for more effective and/or less costly polymers than those commercially available. Chitosan has been used as a flocculant for cells, but has never been applied specifically for crossflow membrane filtration of fermentation broths, or the like, so far as can be determined from the literature.